This invention refers to a band pass and/or elimination network for electric signals, with a high level of efficiency in the selectivity and adjustment processes. This selectivity capacity would only normally be present in considerably more complex devices which complicate the realisation and adjustment processes.
Therefore, this invention improves, and, at the same time, simplifys the filtering process, when compared to other devices which obtain the same results with respect to frequency response.
The invention also refers to a filter network with a high level of immunity against unsuitable frequencies, both for band pass and band elimination filters, this being provided for by a counterphase effect which ensures that these unsuitable frequencies are, in theory, cancelled when they reach the filter output, there being practically no output of such frequencies. This aspect of the invention is described in more detail further on.
The frequency filter network of the invention can be used in L.F. to S.H.F. applications, although its characteristics and size make it particularly suitable for V.H.F. and U.H.F. applications.
Filter devices are currently used in all transmission, teledistribution, radio broadcasting and radio linkage systems, as in all other systems which need to select and obtain information contained in a specific frequency segment. This invention can be used in all of these systems.
In other cases, where it is necessary to process all frequencies with the exception of some or specific segments or bands, band trap or elimination filters are used. In both cases the invention is remarkably efficient, not only in selectivity, but also in affording protection or rejecting the unsuitable frequencies, whatever their strength may be.